The present invention relates to a sensor-mounted roller bearing apparatus in which sensors are installed.
Among roller bearing apparatus, sensor-mounted roller bearing apparatus are provided with sensors for detecting operation data such as loads in the course of bearing rotation besides their original bearing function. For example, Japanese Patent Publication of No. 2003-530565 describes a bearing apparatus applied to the bearing hub unit of a vehicle in which multiple sensor modules having strain gauges attached to the surface of a housing surrounding a bearing ring are provided and loads are detected based on the sensing results from the modules. Japanese Unexamined Patent Application No. 2003-246201 describes a bearing apparatus applied to the bearing hub unit of a vehicle in which strain gauges are attached to the mounting flange of an inner ring (a rotary bearing ring) to detect loads applied to the bearing apparatus.
The bearing apparatus described in Japanese Patent Publication No. 2003-530565 detects loads based on the piezo-resistance effect of strain gauges. Therefore, a dedicated bridge circuit has to be connected to each strain gauge. The resistance of a strain gauge is easily affected by changes in temperature such as the ambient temperature. It is therefore required to compensate for temperature drifts of the gauge resistor by providing a temperature compensation plate near each gauge for accurate load detection. Consequently, it is difficult in this prior art apparatus to reduce the number of parts and simplify the structure.
On the other hand, the bearing apparatus described in Japanese Unexamined Patent Application No. 2003-246201 has strain gauges attached to the mounting flange of the rotary bearing ring. A radio transmitter or a slip ring must be provided to output detection signals from the strain gauges to a control apparatus, which complicates the structure of the bearing apparatus. In this prior art bearing apparatus, through-holes are formed in the mounting flange and the strain gauges are attached to the surface of the through-holes so that the mounting flange is easily deformed (distorted) for accurate load detection, hampering attempts to simplify the assembly of the load sensor.